Space agriculture involves growing plants in extraterrestrial environments to sustain human life and support space missions. The primary objective is to cultivate crops for food and other materials, enabling long-duration human presence beyond Earth and supporting future space exploration and potential colonization.
Why Cultivate Food in Space?
Cultivating food in space offers several benefits for long-duration missions. Fresh food provides necessary nutrients that can degrade in pre-packaged meals, helping astronauts maintain good physical health. The ability to grow food in-flight or at a destination significantly reduces the mass and cost associated with resupply missions from Earth. For example, a 2.5-year crewed Mars mission with four people would require nearly 15,000 pounds of food if all provisions were brought from Earth.
Plants also contribute to regenerative life support systems by producing oxygen through photosynthesis, which helps purify the air in spacecraft and habitats. They can recycle wastewater through transpiration, turning it into clean water for the crew. Beyond the physical benefits, growing plants offers psychological advantages, improving astronaut well-being, mood, and reducing stress and anxiety during prolonged isolation. The presence of fresh greenery provides a calming effect and a connection to Earth, which can be beneficial in austere space environments.
Farming Techniques and Systems
Space agriculture largely relies on soilless cultivation methods within controlled environments.
Hydroponics
This common technique involves growing plants in nutrient-rich water solutions. Plants are supported by inert media such as rock wool or clay pellets, which provide stability and facilitate root development. This method allows for precise control over nutrient delivery and water usage, leading to faster growth rates and higher yields compared to traditional soil-based farming.
Aeroponics
This takes this a step further by suspending plant roots in the air and misting them with a nutrient solution. This approach maximizes oxygen exposure to the roots, which can promote faster growth and enhanced nutrient uptake while using even less water than hydroponics.
Aquaponics
This integrates hydroponics with aquaculture, creating a symbiotic system where fish waste provides natural fertilizer for the plants, and the plants, in turn, filter and clean the water for the fish. This closed-loop system minimizes waste and conserves resources.
These techniques are implemented within closed-loop systems and controlled environment agriculture (CEA) principles. CEA systems manage factors like light, air, and water to optimize plant growth and maximize resource utilization. Such systems are designed to recycle nearly all resources, including water and nutrients, to achieve high yields with minimal waste. The Advanced Plant Habitat (APH) on the International Space Station (ISS) is an example of a growth chamber that utilizes LED lighting and a porous clay substrate with controlled-release fertilizer to deliver water, nutrients, and oxygen to plant roots.
Selecting Plants for Space Environments
Choosing suitable crops for space cultivation involves specific criteria to ensure efficiency and astronaut well-being. Plants are selected based on their high nutritional value, providing essential vitamins and minerals that might be lacking in pre-packaged diets. Fast growth rates and high yields are also important, as space and resources are limited. Crops that produce minimal inedible biomass are preferred to maximize the harvest index and reduce waste.
Adaptability to controlled environments, including responsiveness to specific light spectrums and nutrient solutions, is also considered. Researchers are currently investigating various plants, with leafy greens like lettuce, spinach, Swiss chard, and kale being popular choices due to their quick growth, small space requirements, and ability to be harvested multiple times.
Herbs such as basil, mint, and parsley are also being researched for their flavor and nutritional contributions. Some root vegetables like radishes and carrots, along with certain fruit crops like tomatoes and strawberries, are also under consideration for their potential in space agriculture. NASA’s Veggie system on the ISS has successfully grown “Outredgeous” red romaine lettuce, Mizuna mustard, and Waldmann’s green lettuce.
Cultivating in Unique Space Conditions
Space presents unique environmental challenges that necessitate specific adaptations in cultivation systems.
Microgravity
The near-weightless condition in space significantly affects how water and nutrients behave around plant roots. Unlike on Earth where gravity pulls water downwards, in microgravity, water can form spheres around roots, leading to waterlogging and hindering gas exchange. To counter this, specialized growth media like clay-based pillows are used to distribute water, nutrients, and air evenly around the roots.
Radiation and Light Optimization
Radiation is another concern in space, as cosmic rays can induce mutations in plant genomes and affect growth. While research is ongoing to understand the long-term effects of radiation, systems are designed with protective shielding to mitigate exposure. Light-emitting diodes (LEDs) are also used to mimic natural sunlight, providing the specific wavelengths plants need for photosynthesis while managing energy consumption and heat production.
Resource Recycling
Efficient resource recycling is fundamental to closed-loop space agriculture systems. Water from plant transpiration is collected and purified for reuse, and nutrient solutions are recirculated to minimize waste. Carbon dioxide exhaled by astronauts is absorbed by plants for photosynthesis, and the oxygen produced is then made available for the crew. This continuous recycling of air, water, and nutrients is designed to create a sustainable artificial ecosystem.